1. Field of the Invention
The present invention generally relates to material processing and, more particularly, is concerned with features for controlling the flow of waste materials, such as medical and other waste matter, during pyrolyzing of such materials in a pyrolysis chamber of a material processing apparatus to thereby control residence time of such materials therein and ensure completion of the pyrolyzing of such material in the pyrolysis chamber.
2. Description of the Prior Art
The problem of disposal of waste matter involves a material processing challenge that is becoming increasingly acute. The primary material processing methods of waste disposal have been burning in incinerators and burial in landfills. These two material processing methods have severe disadvantages. Burning of waste liberates particulate matter and fumes which contribute to pollution of the air. Burial of wastes contributes to the contamination of ground water. A third material processing method is recycling of waste. Although increasing amounts of waste are being recycled, which alleviates the problems of the two primary material processing methods, presently available recycling methods do not provide a complete solution to the waste disposal problem.
The problem of disposal of biomedical waste materials is even more acute. The term "biomedical waste materials" is used herein in a generic sense to encompass all waste generated by medical hospitals, laboratories and clinics which may contain hazardous, toxic or infectious matter whose disposal is governed by more stringent regulations than those covering other waste. It was reported in The Wall Street Journal in 1989 that about 13,000 tons a day of biomedical waste, as much as 20% of it infectious, is generated by around 6,800 U.S. hospitals.
Hospitals and other generators of biomedical waste materials have employed three main material processing methods of waste handling and disposal: (1) on-site incineration with only the residue transferred to landfills; (2) on-site steam autoclaving and followed by later transfer of the waste to landfills; and (3) transfer of the waste by licensed hazardous waste haulers to off-site incinerators and landfills. Of these three main material processing methods, theoretically at least, on-site disposal is the preferred one.
However, many hospital incinerators, being predominantly located in urban areas, emit pollutants at a relatively high rate which adversely affect large populations of people. In the emissions of hospital incinerators, the Environmental Protection Agency (EPA) has identified harmful substances, including metals such as arsenic, cadmium and lead; dioxins and furans; organic compounds like ethylene, acid gases and carbon monoxide; and soot, viruses, and pathogens. Emissions of these incinerators may pose a public health threat as large as that from landfills.
Nonetheless, on-site disposal of biomedical waste materials still remains the most promising solution. One recent on-site waste disposal unit which addresses this problem is disclosed in U.S. Pat. No. 4,934,283 to Kydd. This unit employs a lower pyrolyzing chamber and an upper oxidizing chamber separated by a movable plate. The waste material is deposited in the lower chamber where it is pyrolyzed in the absence of air and gives off a combustible vapor that, in turn, is oxidized in the upper chamber. While this unit represents a step in the right direction, it does not appear to approach an optimum solution to the problem of biomedical waste material disposal.
One problem with the approach of the aforementioned patent is that it proposes the use of an on-site waste disposal unit which is dedicated to the disposal of biomedical waste material. This approach requires that more than one incineration system be installed and maintained at hospitals, namely, one for biomedical waste and another for all other hospital waste. Resistance has been encountered to the adoption of this approach by hospitals due to added cost of installation, operation and maintenance. An urgent need has developed for an all-purpose material processing apparatus which can handle disposal of all types of hospital waste materials, both biomedical waste and general waste, such as metal needles and glass and plastic bottles.